Cutting tools that operate by directing a high-intensity energy source such as a high-speed fluid stream along a cutting path in a workpiece are used in many industrial applications to cut various patterns. In simple cutting tools of this kind, the fluid stream is emitted from a stationary nozzle and the workpiece translated to produce the desired cutting path. A similar effect can be achieved by maintaining the workpiece in position and translating the nozzle. Often, it is necessary to make a beveled or angled cut in a workpiece. To produce a beveled cut, the nozzle must be pivoted with respect to the workpiece to change the angle of entry of the fluid jet as it advances along the cutting path. Coordination of translation and pivotal rotation is essential to fast, accurate cutting.
In the field of tuna fish processing, for example, the completely or partly automated cutting of frozen slabs of tuna to remove blood meat and skin portions from edible loin meat portions is described in three U.S. Pat. Nos. (3,800,363; 4,738,004; and Re. 33,917) to James M. Lapeyre and assigned to the assignee of this application. Besides discussing the cutting of tuna slabs along irregular paths, the patents also describe scanners for producing images of one or both sides of the slabs from which control signals are generated to control the cutting apparatus. The two older patents (U.S. Pat. Nos. 3,800,363 and 4,738,004) discuss general methods of visioning and cutting tuna slabs with few details of the conversion of the electrical signals representing the cutting path as determined by the video scan into control signals for the cutting apparatus. Reissued patent Re. 33,917 shows a water jet robot relatively movable with respect to the stationary slab to be cut. None of the patents addresses the problem of achieving fast and accurate cutting paths.
The water jet nozzle on the water jet robot shown in Re. 33,917 is at the end of a sequence of pivot joints having long and massive connecting arms that are unwieldy and slow, exhibiting a lot of inertia, which is detrimental to the rapid direction changes needed for cutting irregular paths and to the overall fast throughput required on a production line. Furthermore, more energy is consumed in powering the motors driving the heavy arms of the robot.
Another shortcoming of the Re. 33,917 robot, which is a standard commercial robot used in many manufacturing fields besides tuna processing and water-jet cutting, is that the pivotal motion provides translation as well as rotation of the water jet with respect to the workpiece. As such, the pivoting of one joint can cause a translation that must be compensated for by pivoting other joints. Consequently, a complex control algorithm is required to coordinate the rotation and translation of the nozzle with respect to the workpiece.
Thus, an object of the present invention is to provide a cutting system capable of rapidly producing beveled cuts in a workpiece in an energy-efficient manner suitable for production-line applications.